1. Field of the Invention
The present invention relates to a drive unit used for a pressure device, such as a spot welding gun, friction stir welding (FSW), and a press.
2. Description of the Related Art
Drive units used for pressure devices, such as a spot welding gun, FSW, and a press, have conventionally been configured to be severally provided with a through-hole formed in the rotary shaft of a motor, which is a drive source, a pressure shaft including a part to be drawn into the through-hole at the time of drive, and an incorporated piezoelectric type load cell, detecting a pressurization quantity. Among them, the drive unit having the structure disclosed in, for example, the following document is known: A. Kirchheim et al., Kistler Instrumente AG, Switzerland, “Manufacturing Force Measurement in Resistance Welding,” Page 10 FIG. 13, [online], 19 DVS-Meeting “Resistance Welding” May 26-27, 2004 Duisburg, Germany, Retrieved from the Internet: <URL: http://www.kistler.com/mediaaccess/920-332e-07.07.pdf>.
Now, because the piezoelectric type load cell is arranged between an output shaft and a bearing in the drive unit of the pressure device mentioned above, the force operating on the piezoelectric type load cell changes to an increasing direction at the time of pressurization. Consequently, the piezoelectric type load cell has the problems, in which the capacity of the load cell is required to have a certain degree of magnitude and it is not easy to attach and remove the load cell.